Top panel: line shift from Fe I spectral lines, estimated using the recalibrated wavelengths, λ_nist, as reference laboratory wavelengths, fitted on HARPS-LFC Moon spectra with 3D line profiles in the blue chip (blue dots) and in the red chip (red dots). Line shifts of the two Fe II lines are displayed as orange symbols. The light blue and light yellow regions show the standard deviation, σ_GRS, 3D, and the . Bottom panel: histogram of the line shifts. The black dashed line shows the theoretical solar GRS. The green dashed-dotted line shows the mean line shift, v_GRS, 3D, of N = 97 lines at 10 < EW [mÅ] < 180.